Sensors and systems for notifying when a wheel of a vehicle is not securely fitted to the vehicle improve safety. Such sensors and systems allow preventative action to be taken prior to a wheel being lost, which prevents accidents and damage to vehicles, pedestrians and street furniture.
One such system is disclosed in WO2011/121334 and comprises a battery, a transmitter and a detector, or switch, operated by a coil spring. However, known sensors and systems are complex and costly to manufacture. Special dynamic seals are required to keep the area housing the electronics free from water ingress, whilst allowing movement of the switch. The complexity of known systems makes them more prone to failure. In addition, known sensors are likely to become damaged during use and maintenance of the vehicles to which they are fitted.